Variable recruitment fluidic artificial muscle (FAM) bundles consist of multiple FAMs arranged in motor units that are sequentially activated as load demand increases. The conventional configuration of a variable recruitment FAM bundle requires a valve for each motor unit, which is referred to as a multi-valve system (MVS). As each motor unit within the bundle is selectively recruited, this configuration is highly adaptable and flexible in performance. However, as the number of motor units increases, the valve network can become complex and heavy in its design. To decrease complexity and weight, the concept of an orderly recruitment valve (ORV) has been proposed and analyzed. The ORV allows multiple motor units to be controlled using a single valve that recruits and pressurizes all motor units. The ORV concept consists of a spool valve with multiple outlet ports and a motor unit connected to each port. A linear actuator controls the position of the spool, allowing fluid flow into each port in succession. Naturally, de-recruitment happens in reverse order. The objective of the ORV is to strike a balance between performance and compactness of design. The purpose of this paper is to present analytical modeling that can be used to understand the behavior and performance of an ORV system and develop an experimental proof-of-concept that illustrates the ORV operation in hardware. A pneumatic ORV prototype was constructed and used to actuate two FAMs sequentially, each representing a motor unit. The results demonstrate the ORV as a compact system with which a variable recruitment bundle with multiple recruitment states can be controlled.

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